Yen to tuck into ice-creams - source of some reticence (7)
I believe the answer is:
Here is my best explanation:
'reticence' is the definition.
(I have seen 'Arch reticence ' mean 'coyness' so perhaps 'reticence' could also mean 'coyness')
'yen to tuck into ice-creams source of some' is the wordplay.
'yen' becomes 'y'.
'to tuck into' is an insertion indicator.
'ice-creams' becomes 'cones' (ice-cream cones).
'source of' indicates taking the first letters.
The first letter of 'some' is 's'.
'y' put inside 'cones' is 'coynes'.
(Other definitions for coyness that I've seen before include "Demureness", "Modesty", "Arch reticence", "Pretended modesty", "Affected modesty", "evasive quality" and "Shyness".)